AbstractHabitat fragmentation increases forest edges, which in turn influence the microclimate to which ferns are exposed. Ferns do not depend on pollinators or dispersers, which make abiotic variables responsible for triggering the manifestation of their phenophases. Phenology has been an important tool in understanding the effects of habitat fragmentation on plant behaviour. Our aims were to compare the phenology of populations of the fern Ctenitis submarginalis at a natural edge, an artificial edge and in the forest interior and determine whether the edge effect has an influence. Populations of C. submarginalis were monitored in these three subareas of an Araucaria forest for 2 years. Relative air humidity, air temperature, precipitation, photosynthetically active radiation, photoperiod and soil moisture were monitored concomitantly with the collection of phenological data in each subarea. Among the populations, that of the artificial edge had the greatest number of individuals and the highest intensity of sporangium formation and leaf senescence. Only the reproductive event (sporangium formation) of populations of all subareas was seasonal. The forest interior populations had the highest seasonality of sporangium formation. Ferns at forest edges (natural and artificial) were more affected by the edge effect than those of the forest interior. Abiotic variables that are more sensitive to alterations by the edge effect, such as relative air humidity, soil moisture and temperature, influenced vegetative events at edges. On the other hand, photoperiod, which is constant from year to year, overlapped the influence of the other environmental factors in the forest interior. Thus, we evidenced heterogeneity in the phenological responses of ferns at forest edges.